A method and device which provides a non-volatile memory cell capable both of volatile dynamic random access memory (DRAM) storage and non-volatile electrically erasable programmable read-only memory (EEPROM) storage is described in the related co-pending application U.S. Ser. No. 654,332, filed Sept. 24, 1984, on behalf of Patrick Chuang, Robert Yau and Ron Maltiel entitled "An Improved Non-Volatile Dynamic RAM Cell", and that description is hereby incorporated by reference in the instant application. The memory cell disclosed in the related, co-pending application is a non-volatile dynamic RAM (NVDRAM) which operates as an ordinary dynamic RAM cell in one mode of operation, and as a non-volatile ROM cell in another mode of operation.
A shadow memory array composed of a number of NVDRAM cells which can store and compare volatile and non-volatile data is useful in pattern recognition and instrument calibration. However, in the prior art, when recalling the data stored in the non-volatile portion, from the so-called "shadow memory", the data stored in the volatile memory is lost.